1. Field of the Invention
The present invention relates to solid state relays such as Triac output, MOS output or IGBT output, provided in various types of electronic devices as switching elements. The present invention relates especially to solid state relays best suited for electronic devices such as power supply devices, household electrical appliances, inverter control devices, and the like having circuits that transmit signals while electrically isolating input from the output.
2. Description of the Related Art
As shown in FIG. 12, for example, a conventional solid state relay is formed by mounting a light coupling element 91, a switching element 93 such as a transistor, a Triac, an IGBT, or a C-MOS switching element electrically connected to a light-receiving portion on the light coupling element 91, a chip resistor 94 serving as a protective element on the output side, a chip capacitor 95, and a chip resistor 96 serving as an LED limiting resistor (protective element on the input side) inside the light coupling element 91, on a metallic lead 92 with silver paste or high temperature solder, for example, and sealing with a black light blocking resin 97 in order to protect a chip mounting portion, ensure electrical isolation, and protect the light coupling element 91 from external stray light.
Here, in the light coupling element 91, a light path is formed by mounting an LED (used as a light-emitting element) and a photodiode, a phototransistor, a phototriac, a photovoltaic, or the like (used as a light-receiving element) on two opposing lead frames and sealing the two lead frames by a translucent resin, for example.
It should be noted that conventional solid state relays as described above are also disclosed in JP 2001-127099A and JP H5-206504A, for example.
However, in the above-described conventional solid state relay in which the light-emitting element, the light-receiving element, the switching element, and the protective elements such as the chip resistor and the chip capacitor are mounted, the two lead frames on which the light-emitting element and the light-receiving element are respectively mounted are first placed in opposition to each other and sealed with resin through transfer molding, for example, to fabricate the light coupling element, and this light coupling element, the switching element, and the protective elements are then mounted on a substrate of still another lead frame, for example, after which the substrate is sealed by resin.
In such a conventional method, the number of resin sealing steps and part mounting steps increases, and the degree of integration decreases. Thus, there is the problem that the costs rise and also the package size of the device becomes large.
The present invention was achieved in view of this situation, and it is an object of the present invention to provide a solid state relay that allows a simplification of the assembly steps and a miniaturization of the device.